Conventional power supply apparatuses comprise a resonant circuit (for example, see Patent Literature 1).
A wireless power transmission device of Patent Literature 1 comprises a resonant circuit. The wireless power transmission device comprises a resonant circuit and a variable voltage source. Moreover, the resonant circuit includes an inductor and a plurality of capacitors, the plurality of capacitors being configured to include a varicap. Moreover, the varicap has a property where a capacitance value decreases when a voltage value applied from the variable voltage source increases. As a result, this wireless power transmission device is able to adjust a resonant frequency established by an inductance of the inductor and a capacitance value (synthesized capacitance value) of the plurality of capacitors by adjusting the voltage value of the variable voltage source. As a result, even in a situation where the resonant frequency of the resonant circuit and a frequency of a drive signal of the variable voltage source are different (shifted), by adjusting the voltage value applied to the varicap, it becomes possible to make the resonant frequency of the resonant circuit and the frequency of the drive signal substantially equal.
Therefore, the wireless power transmission device of Patent Literature 1 is able to efficiently transmit power to a power receiving apparatus even in a situation where there is a shift in the resonant frequency of the resonant circuit due to the capacitance value (capacitance) of the capacitors of the resonant circuit having variability with regard to a design value.